1. Field
This disclosure is concerned generally with compositions useful for controlling endoparasites in horses and specifically with a paste-like preparation of trichlorfon which demonstrates a high degree of stability and bioavailability.
2.Prior Art
Trichlorfon (O,O-Dimethyl-1-hydroxy-2,2,2-trichloroethylphosphonate) is a well known and proven anthelmintic and boticide in the horse. The compound is described in U.S. Pat. No. 2,701,255 to Lorenz. Trichlorfon is commonly available commercially in a dry form (e.g. Anthon.RTM. horse anthelmintic) from which a liquid formulation can be readily prepared. Unfortunately, the shelf life of available forms of trichlorfon is limited and it is known that presently available trichlorfon will degrade with time. Also, presently available forms of trichlorfon limit its bioavailability over prolonged periods of time.
Although other equine parasiticidal preparations in paste form have been disclosed (i.e. U.S. Pat. No. 3,746,490 to Marsland et al disclosing a resin-based paste formulation of the liquid dimethyl-2,2-dichlorovinyl phosphate or DDVP), we are unaware of any prior disclosure of a trichlorfon paste. We have prepared a paste-like formulation of trichlorfon which not only appears to have an infinite shelf life under normal storage conditions of 25.degree.-30.degree. C. but, quite surprisingly, a higher degree of bioavailability at lower dosage rates than other forms of the same compound. Details of our formulation are described herein.